Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $206.94   11.482%   $230.7009   $230.70   $230.70   $230.70  
  Purchase #2 $170.58   11.763%   $190.6453   $190.65   $190.65   $190.60  
  Purchase #3 $150.94   3.654%   $156.4553   $156.46   $156.45   $156.50  
  Purchase #4 $98.66   10.202%   $108.7253   $108.73   $108.75   $108.70  
  Purchase #5 $69.48   11.372%   $77.3813   $77.38   $77.40   $77.40  
  Purchase #6 $237.34   10.508%   $262.2797   $262.28   $262.30   $262.30  
  Purchase #7 $116.93   7.507%   $125.7079   $125.71   $125.70   $125.70  
  7 purchase totals = $1,050.87       $1,151.8957   $1,151.91   $1,151.95   $1,151.90